1. Field of the Invention
The present invention generally relates to a metal/ceramic bonding article having a ceramic substrate and a metal plate of an overall-rate solid solution type alloy bonded directly to the ceramic substrate, and a method for producing the same. More specifically, the invention relates to an electronic member for resistance wherein a metal plate of a copper containing alloy, such as a copper-nickel or copper-nickel-manganese alloy, is bonded directly to a ceramic substrate as a resistor, and a method for producing the same.
2. Description of the Prior Art
As an example of a method for bonding a metal plate directly to a ceramic substrate, there is known a method for bonding a copper plate directly to an oxide ceramic substrate (e.g., an alumina substrate) by utilizing an eutectic melt of copper with oxygen. Metal/ceramic bonding articles produced by such a method are utilized as electronic circuit boards or the like (see U.S. Pat. No. 3,994,430). In this technique, an element forming an eutectic with a certain metal is added to the metal or incorporated into the metal from a bonding atmosphere, to utilize an eutectic melt of the metal with the element as a bonding binder at a temperature of a melting point of the metal or lower and at a temperature of an eutectic point or higher. However, in this method, there is a problem in that the metal or alloy capable of being bonded directly to the ceramic as a solid is limited to a metal capable of forming an eutectic melt.
There are known methods for bonding a metal plate to a ceramic substrate via a brazing filler metal as an intermediate material. For example, there is known a method for bonding a copper plate to a ceramic substrate by adding an active metal, such as titanium or zirconium, to a silver-copper brazing filler, and copper/ceramic bonding articles produced by such a method are also utilized as electronic circuit boards or other structural articles (see Japanese Patent Laid-Open No. 10-251075). In these bonding articles, the element, such as titanium or zirconium, which is an active metal in the brazing filler metal, reacts with the components of the ceramic to produce reaction products on the interface between copper plate and the ceramic substrate to bond the copper plate to the ceramic substrate. Therefore, the copper plate is not bonded to the ceramic substrate unless the active metal is used. In this method, there are problems in that it is required to use a noble metal, such as silver, in the brazing filler metal and to produce the bonding article in a high vacuum state, so that the producing costs are relatively high. There is also a problem in that this method can not be applied to bonding for an electronic member for resistance since the value of resistance of the electronic member varies by alloying with the brazing filler metal.
Moreover, there is known a so-called molten metal bonding method comprising the steps of melting a metal in a non-oxidizing atmosphere to cause the metal to directly contact a ceramic substrate, and moving the metal to remove an oxide film and so forth on the surface thereof to bond the metal directly to the ceramic substrate (Japanese Patent Laid-Open No. 7-276035). In theory, the molten metal on the fresh surface of the metal is moved in a non-oxidizing atmosphere to cause the active surface of the metal to contact the ceramic substrate to bond the metal directly to the ceramic substrate. In this technique, all the metal to be bonded is first melted, so that it is required to previously prepare a mold or die having a predetermined shape which is a target shape after bonding. Metal/ceramic bonding articles produced by this method are also utilized as electronic circuit boards or the like. However, in this method, since the metal is melted to be cast, there are problems in that it is difficult to prepare electronic materials, such as vary thin resistors, and the producing costs increase.
On the other hand, a copper-nickel alloy is known as the material of a resistor, and constantan and manganin are used as the materials of fine resistors for electrometers, compensating lead wires, piezoresistance stress meters and so forth. These alloys are used as wire materials or applied on organic films as gages.
However, if a resistor is prepared by any one of the above described conventional methods, there is a problem in that it is difficult to precisely measure the value of resistance of the resistor due to the generation of heat.